Multimeric elp fusion constructs

ABSTRACT

ELP fusion proteins, multimeric ELP spider complexes formed of ELP fusion proteins, and methods of using the same. The construct may be in the form of an ELP spider structure complex including multi-leg moieties comprising ELP fusion proteins capable of forming covalent disulfide bonds. The multimeric fusion constructs may be employed in peptide production and purification and/or to enhance proteolytic resistance of a protein or peptide moiety in a fusion construct, by provision of the fusion protein in an ELP spider complex.

CROSS-REFERENCE TO RELATED APPLICATION

The benefit of priority of U.S. Provisional Patent Application 60/756,269 filed Jan. 4, 2006 in the name of Suzanne Dagher is hereby claimed under the provisions of 35 USC 119(e). The disclosure of such Provisional Patent Application 60/756,269 is hereby incorporated herein by reference, in its entirety.

FIELD OF THE INVENTION

The present invention relates to fusion constructs comprising multimeric elastin-like peptides (ELPs) having utility, inter cilia, in biopharmaceutical applications, and to methods of making and using the same.

DESCRIPTION OF THE RELATED ART

U.S. Pat. No. 6,852,834 issued Feb. 8, 2005 in the name of Ashutosh Chilkoti for “FUSION PEPTIDES ISOLATABLE BY PHASE TRANSITION” and U.S. patent application Ser. No. 11/053,100 filed Feb. 8, 2005 for “FUSION PEPTIDES ISOLATABLE BY PHASE TRANSITION,” in the name of Ashutosh Chilkoti (published Nov. 17, 2005 as U.S. Patent Publication No. 2005/0255554) disclose fusion proteins exhibiting a phase transition. Such fusion proteins comprise a biologically active molecule joined to one or more phase transition protein(s), where the one or more phase transition protein(s) comprise polymeric or oligomeric repeats of a polypeptide sequence. The fusion protein may also, optionally, contain a spacer sequence between the biologically active molecule and the one or more phase transition protein(s).

The biologically active molecules in these constructs can be of widely varying types, including, for example, peptides, non-peptide proteins, lipids, oligonucleotides and carbohydrates, or alternatively a ligand-binding protein or an active fragment thereof having binding affinity to a biomolecule selected from the group consisting of small organic or inorganic molecules, proteins, peptides, single-stranded or double-stranded oligonucleotides, polynucleotides, lipids, and carbohydrates.

The phase transition can be mediated by one or more techniques such as changing temperature, changing pH, addition of solutes and/or solvents, side-chain ionization or chemical modification and/or changing pressure.

The one or more one or more protein(s) exhibiting phase transition behavior can include polymeric or oligomeric repeats of the pentapeptide Ile-Pro-Gly-X-Gly or Leu-Pro-Gly-X-Gly, wherein X is any natural or non-natural amino acid residue, and wherein X optionally varies among polymeric or oligomeric repeats.

The technology disclosed by the above-identified Chilkoti patent and application includes methods of purification of fusion proteins to yield a protein of interest, by forming a polynucleotide comprising a nucleotide sequence encoding a fusion protein exhibiting a phase transition, expressing the fusion protein in culture, and subjecting a fusion protein-containing material from the culture to processing involving centrifugation and inverse transition cycling to recover the protein of interest.

The Chilkoti technology reflects an initial discovery that non-chromatographic, thermally-stimulated phase separation and purification of recombinant proteins can be easily achieved by forming fusion proteins that contain the target recombinant proteins with N- or C-terminal elastin-like polypeptide (ELP) tags.

ELPs are repeating peptide sequences that have been found to exist in the elastin protein. Among these repeating peptide sequences are polytetra-, polypenta-, polyhexa-, polyhepta-, polyocta, and polynonapeptides.

ELPs undergo a reversible inverse temperature transition: they are structurally disordered and highly soluble in water below a transition temperature (T_(t)), but exhibit a sharp (2-3° C. range) disorder-to-order phase transition when the temperature is raised above T_(t), leading to desolvation and aggregation of the polypeptides. The ELP aggregates, when reaching sufficient size, can be readily removed and isolated from solution by centrifugation. More importantly, such phase transition is reversible, and the isolated ELP aggregates can be completely resolubilized in buffer solution when the temperature is returned below the T_(t) of the ELPs.

It was a surprising and unexpected discovery that fusion proteins (“FP's”) containing target recombinant proteins with N- or C-terminal ELP tags also undergo a thermo-dependent phase transition similar to that of free ELPs.

This discovery has been particularly useful for non-chromatographic, thermally-stimulated separation and purification of recombinant proteins. By fusing a thermally responsive ELP tag to a target protein of interest, environmentally sensitive solubility can be imparted to such target protein. Target proteins are readily expressed as soluble fusion proteins with N- or C-terminal ELP sequences in host organisms such as E. coli, wherein the fusion proteins exhibit a soluble-insoluble phase transition when the temperature is raised from below T_(t) to above T_(t). This inverse phase transition is exploited for purifying the target proteins from other soluble proteins produced by the organism, by nonchromatographic “inverse transition cycling” (ITC) separation.

The fundamental principle of ITC thus is remarkably simple. It involves forming an ELP fusion protein as described hereinabove, which contains the target protein with a N- or C-terminal ELP tag, rendering the ELP fusion protein insoluble in aqueous solution by triggering its inverse phase transition. This can be accomplished either by increasing the temperature above the T_(t) or alternatively by depressing the T_(t) below the solution temperature by the addition of NaCl or other salt or solute, organic or inorganic, to the solution. This results in aggregation of the ELP fusion protein, allowing it to be collected by centrifugation or other weight- and/or size-dependent mass separation techniques, e.g., membrane separation or filtration.

The aggregated ELP fusion protein can then be resolubilized in fresh buffer solution at a temperature below the T_(t), thereby reversing the inverse phase transition, to yield soluble, functionally active, and purified fusion protein.

Successive purification steps may also be carried out using ITC to achieve a highly pure, e.g. ultrapure, fusion protein product. Furthermore. ITC may also be used to concentrate and exchange buffers if desired as follows: the purified protein is aggregated by triggering the phase transition, and resolubilized in a smaller volume than before inducing the phase transition to concentrate the protein solution, and buffer exchange is achieved by simply resolubilizing the protein in a buffer of different composition than the starting buffer.

Free target protein then can be obtained, for example, by carrying out protease digestion or other scission process at an engineered recognition site located between the target protein and the ELP tag, followed by a final round of ITC to remove the cleaved ELP tag and yield the purified free target protein.

The advantage of the use of inverse phase transition cycling is that purification of the protein of interest is facilitated in a ready and efficient manner. Protein production and purification efficiency are of continuing interest in ongoing efforts to refine and develop this technology, involving the search for new constructs that are well-adapted to the inverse phase transition cycling process, to yield proteins of interest at high yields. The present invention provides such new constructs.

SUMMARY OF THE INVENTION

The present invention is based on the discovery of new protein constructs that are easier to purify, enable production of peptide or protein products in higher amounts and are less susceptible to proteolysis, as compared to the single ELP-based constructs of the prior art. Such constructs are useful in inverse phase transition processes.

Thus in one embodiment, the invention provides a fusion protein exhibiting a phase transition, including at least one target protein or peptide, one or more proteins comprising oligomeric repeats of a polypeptide sequence, wherein the one or more proteins exhibits a phase transition and are joined to the at least one target protein or peptide, at least two residues capable of forming a disulfide bond and optionally a spacer sequence separating any of the phase transition protein(s) front any of the target protein(s) or peptide(s). The invention also provides a polynucleotide encoding such a fusion protein, an expression vector comprising such a polynucleotide and a host cell that expresses the fusion protein.

In another embodiment the invention provides ELP spider complex comprising two or more fusion proteins exhibiting a phase transition, including at least one target protein or peptide, one or more proteins comprising oligomeric repeats of a polypeptide sequence, wherein the one or more proteins exhibits a phase transition and are joined to the at least one target protein or peptide, at least two residues capable of forming a disulfide bond and optionally a spacer sequence separating any of the phase transition protein(s) from any of the target protein(s) or peptide(s), wherein the two or more fusion proteins exhibiting a phase transition are linked by at least one disulfide bond.

In still another embodiment the invention provides methods of providing a purified protein of interest and of enhancing proteolytic resistance of a protein or peptide moiety.

The method of the invention providing a purified protein of interest comprises contacting a fusion protein comprising the protein of interest and an ELP tag, wherein the fusion protein contains at least one cleavage site that is cleavable to yield the protein of interest as a cleavage product with ELP-TEV1 that is effective to cleave the cleavage site, thereby yielding said protein of interest as a cleavage product in a cleavage product mixture comprising said ELP rag, any uncleaved fusion protein and said ELP-tagged cleavage agent; and separating the protein of interest from the cleavage produce mixture by inverse phase transition.

In another aspect the invention provides a method of enhancing proteolytic resistance of a protein or peptide moiety in an ELP-based fusion peptide, comprising provision of the ELP-based fusion peptide in an ELP spider complex.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic representation of an ELP fusion protein including a -Cys-Cys-moiety after the ELP and before the TEV site and the peptide. FIG. 1B is a schematic representation of a corresponding spider construct, for pET17b-SD34-ELP4-60-Orexin B (as set forth below in Example 1), and transformation into a BL21 trxB-strain, allowing disulfide bond formation between the fusion proteins to take place in the cytoplasm.

FIG. 2 is an SDS-PAGE gel comparison for ELP4-60-Orexin B (Normal) and ELP4-60-S-S-Orexin B (Spider) (Lane 1: ELP4-60-Orexin B or ELP4-60-S-S-Orexin B; Lane 2: +ELP1-90-TEV; Lane 3: insolubles following T_(t) (I); and Lane 4: solubles following T_(t) (S)).

FIG. 3 shows an LC-MS analysis of Orexin B derived from ELP4-60-Orexin B (FIG. 3A), in which the level of Orexin B was too low to detect by LC-MS, so that the theoretical location was estimated by location of Orexin B in (B) and ELP4-60-S-S-Orexin B (FIG. 3B), 85% pure, in which the major peak contains the correct molecular weight of Orexin B and the minor peak is a proteolytic fragment of Orexin B.

FIG. 4 is a SDS-PAGE gel analysis, showing that the spider influences the amount of purification, the cleavage with ELP4-60-TEV and proteolysis, with all samples being reduced with DTT prior to loading on the SDS-gel.

FIG. 5 is an SDS-PAGE gel analysis of ELP-spider constructs of three additional peptides (Lane 1: ELP4-60-S-S-peptide (reduced with DTT); Lane 2: +ELP1-90-TEV; Lane 3: insolubles following T_(t) (1); and Lane 4: solubles following T_(t) (S)).

FIG. 6 shows LC-MS analysis for non-spider peptides, MMN from ELP4-60-S-S-MMN: 99.3% pure 13 mg/L (FIG. 6A) and NPY from ELP4-60-S-S-NPY: 98.1% pure 20 mg/L (FIG. 6B).

FIG. 7 shows LC-MS analysis for pro-CT from ELP1-90-pro-CT: 98.0% pure (FIG. 7A) and Leptin from ELP1-90-Leptin: 85% pure (FIG. 7B).

FIG. 8 shows the results of testing of spider constructs grown in Example 8, as compared to non-spider constructs containing IFNa2bSD, in order to determine which were most likely to produce soluble protein.

FIG. 9 shows re-expression of selected constructs from FIG. 8. The results of the re-expression show that spider constructs clearly express more target protein than non-spider constructs.

FIG. 10 shows expression of purified target protein obtained after cleavage of each of the constructs. It is shown that the spider constructs express more soluble ELP fusion protein and more IFNa2bSD than non-spider constructs.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS THEREOF

The present invention relates to multimeric elastin-like peptide (ELP) constructs having utility for biopharmaceutical applications, and methods of making and using the same.

The disclosures of the following U.S. patent and U.S. patent application are hereby incorporated herein by reference in their respective entireties: U.S. Pat. No. 6,352,834 issued Feb. 8, 2005 in the name of Ashutosh Chilkoti for “FUSION PEPTIDES ISOLATABLE BY PHASE TRANSITION” and U.S. patent application Ser. No. 11/053,100 filed Feb. 8, 2005 for “FUSION PEPTIDES ISOLATABLE BY PHASE TRANSITION,” in the name of Ashutosh Chilkoti (published Nov. 17, 2005 as U.S. Patent Publication No. 2005/0255554).

The present invention represents the discovery that multimeric ELP-peptide or ELP-protein constructs can be formed that in relation to single ELP-based peptide or protein constructs of the prior art: (i) can be more easily purified, (ii) enable production, e.g., in a suitable host such as F coli, of peptide or protein products in higher amounts, reflecting enhanced stability in relation to single ELP-based peptide or protein constructs, and (iii) are less susceptible to proteolysis.

As used herein, the term “spider construct” is used to refer to fusion proteins capable of forming multimeric or multi-legged spider complexes of the present invention. Spider constructs differ from single ELP-based constructs in that they are capable of forming covalent crosslinks in the form of disulfide bonds, linking them to other spider constructs and forming spider complexes. Such disulfide bonds are often formed between cysteine residues of the spider constructs. Cysteine residues present in a construct of the invention may be added to the construct on either side of the ELP or may be found within the ELP itself. Cysteines adjacent to the ELP in the construct may be on either the C-terminal or N-terminal end of the ELP, regardless of whether the ELP is oriented to the amino or carboxyl end of the protein or peptide.

A “spider complex” of the invention contains at least two spider constructs linked by at least one disulfide bond, but is not limited by any maximum number of spider constructs or any maximum number of disulfide bonds.

Therefore in one embodiment the invention provides a fusion protein of spider construct comprising

-   -   a) at least one target protein or peptide;     -   b) one or more proteins comprising oligomeric repeats of a         polypeptide sequence, such as those hereinafter described,         wherein the one or more proteins exhibit a phase transition and         are joined to the at least one target protein or peptide of a);     -   c) at least two residues capable of forming a disulfide bond;         and     -   d) optionally, a spacer sequence separating any of the phase         transition protein(s) of b) from any of the target protein(s) or         peptide(s) of a).

The fusion protein of the invention contains a target protein or peptide. More preferably, the target protein or peptide comprises a polypeptide protein, most preferably a biologically active polypeptide, e.g. a therapeutic peptide, protein or an enzyme useful in industrial biocatalysis. Suitable proteins include those of interest in medicine, agriculture and other scientific and industrial fields, particularly including therapeutic proteins such as erythropoietins, interferons, insulin, monoclonial antibodies, blood factors, colony stimulating factors, growth hormones, interleukins, growth factors, therapeutic vaccines, calcitonins, tumor necrosis factors (TNF), and enzymes. Specific examples of such therapeutic proteins include, without limitation, enzymes utilized in replacement therapy; hormones for promoting growth in animals, or cell growth in cell culture; and active proteinaceous substances used in various applications, e.g., in biotechnology or in medical diagnostics. Specific examples include, but are not limited to: superoxide dismutase, interferon, asparaginease, glutamase, arginase, arginine deaminase, adenosine deaminase ribonuclease, trypsin, chromotrypsin, papin, insulin, calcitonin, ACTH, glucagon, somatosin, somatropin, somatomedin, parathyroid hormone, erthyropoietin, hypothalamic releasing factors, prolactin, thyroid stimulating hormones, endorphins, enkephatins, and vasopressin.

The target protein or peptide may also comprise a ligand-binding protein or an active fragment thereof, such as an antibody or antibody fragment, which has specific affinity for a protein of interest. Upon binding to the protein of interest, the fusion protein preferably retains some or all of its phase transition character, so that the protein of interest bound to such fusion protein may be isolated by inverse phase transition. In another embodiment the target protein or peptide may be selected from the group consisting of proteins, lipids, carbohydrates, and single- or double-stranded oligonucleotides.

In various embodiments of the invention, the target protein or peptide may be, but is not limited to, IFNa2b, Orexin-B, MMN, NPY, Gh or active fragments thereof.

In addition to the target protein or peptide component, a fusion protein of the invention also includes one or more ELPs exhibiting a phase transition. These ELPs may be of any suitable type.

As used herein, ELPs are repeating peptide sequences that exist in the elastin protein. Among these repeating peptide sequences are polytetra-, polypenta-, polyhexa-, polyhepta-, polyocta, and polynonapeptides.

The ELPs may comprise polymeric or oligomeric repeats of various tetra-, penta-, hexa-, hepta-, octa-, and nonapeptides, including but not limited to VPGG (SEQ ID NO: 1), IPGG (SEQ ID NO: 2), XGVPG (SEQ ID NO: 3), VGVPG (SEQ ID NO: 4), VPAVG (SEQ ID NO: 5), GVGIP (SEQ ID NO: 6), VGLPG (SEQ ID NO: 7), VPGXG (SEQ ID NO: 8). AVGVP (SEQ ID NO: 9), IPGVG (SEQ ID NO: 10). IPGXG (SEQ ID NO: 11), LPGVG (SEQ ID NO: 12), LPGXG (SEQ ID NO: 13). VAPGVG (SEQ ID NO: 14). GVGVPGVG (SEQ ID NO: 15), VPGFGVGAG (SEQ ID NO: 16), and VPGVGVPGG (SEQ ID NO: 17). It will be appreciated by those of skill in the art that the ELPs need not consist of only polymeric or oligomeric sequences as listed hereinabove, in order to exhibit the desired phase transition, and that other polymeric or oligomeric sequences of varying size and constitution that exhibit phase transition behavior are also usefully employed in the broad practice of the present invention.

In one embodiment, the ELPs are polymeric or oligomeric repeats selected from one of the above listed polypentapeptides. Where the above polypentapeptides contain a guest residue X, X may be any amino acid that does not eliminate the phase transition characteristics of the ELP. X may be a naturally occurring or non-naturally occurring amino acid. For example, X may be selected from the group consisting of: alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine and valine. In one aspect of the invention, where the ELP is VPGXG (SEQ ID NO: 8), X is not proline.

X may be a non-classical amino acid. Examples of non-classical amino acids include: D-isomers of the common amino acids, 2,4-diaminobutyric acid, α-amino isobutyric acid, 4-aminobutyric acid, Abu, 2-amino butyric acid, γ-Abu, ε-Ahx, 6-amino hexanoic acid, Aib, 2-amino isobutyric acid, 3-amino propionic acid, ornithine, norleucine, norvaline, hydroxyproline, sarcosine, citrulline, homocitrulline, cysteic acid, t-butylglycine, t-butylalanine, phenylglycine, cyclohexylalanine, β-alanine, fluoro-amino acids, designer amino acids such as β-methyl amino acids, C α-methyl amino acids, N α-methyl amino acids, and amino acid analogs in general.

In one embodiment, the ELP is a “Series I” pentapeptide of repeating oligomer XGVPG (SEQ ID NO: 3) where X is independently selected from Val, Gly and Ala, in a ratio of 5V:3G:2A, selected from ELP1-90 and ELP1-180.

In another embodiment, the ELP is a “Series II” pentapeptide of repeating oligomer XGVPG (SEQ ID NO: 3) where X is independently selected from Lys, Val and Phe, in a ratio of 1K:2V:1F, selected from ELP2-64 and ELP2-128.

In still another embodiment of the invention, the ELP is a “Series III” pentapeptide of repeating oligomer XGVPG (SEQ ID NO: 3) where X is independently selected from Lys, Val and Phe, in a ratio of 1K:7V:1F, selected from ELP3-72 and ELP3-144.

In a further embodiment, the ELP is a “Series IV” pentapeptide of repeating oligomer VGVPG (SEQ ID NO: 4), selected from ELP4-60 and ELP4-120.

In a further embodiment, the ELP is a “Series V” pentapeptide of repeating oligomer VPAVG (SEQ ID NO: 5), selected from ELP5-15, ELP5-30 and ELP5-60.

In a further embodiment, the ELP is a “Series VI” pentapeptide of repeating oligomer GVGIP (SEQ ID NO: 6), selected from ELP6-15. ELP6-30 and ELP6-60.

In a further embodiment, the ELP is a “Series VII” pentapeptide of repeating oligomer VGLPG (SEQ ID NO: 7), selected from ELP7-15, ELP7-30 and ELP7-60.

Alternatively, such ELPs can be polymeric or oligomeric repeats of the pentapeptide IPGXG (SEQ ID NO: 11) or LPGXG (SEQ ID NO: 13), where X is as defined hereinabove.

Therefore in one embodiment of the invention, the fusion protein contains a phase transition protein selected front the group consisting of: SEQ ID NO: 1-17.

In another embodiment of the invention, the fusion protein contains a phase transition protein selected from the group consisting of: SEQ ID NOs: 1, 2, 8, 9, 10, 11, 12, 13, 14, 15, 16, and 17.

In still another embodiment, the fusion protein contains a phase transition protein selected from the group consisting of: SEQ ID NOs: 1, 2, 9, 10, 11, 12, 13, 14, 15, 16, and 17.

A further embodiment of the invention relates to a fusion protein containing a phase transition protein, wherein the phase transition protein is selected from the group consisting of: ELP1-90. ELP1-180, ELP2-64, ELP2-128, ELP3-72, ELP3-144, ELP4-60, ELP4-120, ELP5-15, ELP5-30, ELP5-60, ELP6-15, ELP6-30, ELP6-60, ELP7-15, ELP7-30 and ELP7-60.

In the fusion protein the phase transition protein is joined to the at least one target protein or peptide. Such joining may be on either end of the target protein or peptide, forming either an N- or C-terminal ELP tag.

The fusion protein of the invention contains at least two residues capable of forming a disulfide bond. In one aspect this comprises the presence of two cysteine residues within the ELP monomer sequence. In another aspect the cysteines are located elsewhere in the fusion protein, either adjacent to the ELP, or separated from the ELP. The cysteines may be located on either side of the ELP within the fusion protein.

An example of an ELP containing two cysteines within the monomer sequence is set forth below. In the example, the ELP is of a general form “ELPx-y”, where x is an indicator of the ELP series and y is the number of oligomeric repeats. In the following exemplified sequence, the ratio of G:V:C:A is 2:5:2:2.

 G  V  G  V  P  G  V  G  V  P  G  C  C  V  P (SEQ ID NO: 18) GGCGTGGGTGTTCCGGGCGTGGGTGTTCCGGGTTGCTGCGTGCC (SEQ ID NO: 19)  G  A  G  V  P  G  V  G  V  P  G  V  G  V  P  G  V  G  V  P  GGGCGCAGGTGTTCCTGGTGTAGGTGTGCCGGGTGTTGGTGTGCCGGGTGTTGGTGTACC   G  G  G  V  P  G  A  G  V  P  G  G  G  V  P  G AGGTGGCGGTGTTCCGGGTGCAGGCGTTCCGGGTGGCGGTGTGCCGGGC . . .

Another example of an ELP containing two cysteines within the monomer sequence is set forth below, where the ratio of G:V:C:A is 1:5:2:2.

 G  V  G  V  P  G  V  G  V  P  G  C  G  V  P (SEQ ID NO: 20) GGCGTGGGTGTTCCGGGCGTGGGTGTTCCGGGTTGCGGGGTGCC (SEQ ID NO: 21)  G  A  G  V  P  G  V  G  V  P  G  V  G  V  P  G  V  G  V  P GGGCGCAGGTGTTCCTGGTGTAGGTGTGCCGGGTGTTGGTGTGCCGGGTGTTGGTGTACC  G  C  G  V  P  G  A  G  V  P  G  G  G  V  P  G AGGTTGCGGTGTTCCGGGTGCAGGCGTTCCGGGTGGCGGTGTGCCGGGC . . .

The phase transition of the fusion protein is preferably mediated by one or more mechanisms selected from, but not limited to, changing temperature, changing pH, addition of (organic or inorganic) solutes and/or solvents, side-chain ionization or chemical modification, irradiation with electromagnetic waves (rf, ultrasound, and light) and changing pressure. The preferred mechanisms for mediating the phase transition are raising temperature and adding solutes and/or solvents.

Optionally, the fusion protein may contain a spacer sequence separating the phase transition protein from the target protein or peptide. The spacer sequence, when present, preferably comprises a cleavage site, e.g., a proteolytic cleavage site, a chemical cleavage site, a photolytic cleavage site, a thermolytic cleavage site, or a cleavage site susceptible to cleavage in the presence of a shear force, pH change, enzymatic agent, ultrasonic or other predetermined frequency field providing energy effective for cleavage. The cleavage modality may be of any of widely varying types, it being necessary only that the cleaving step yield at least one biological molecule (as a cleavage product) that retains functional utility for its intended purpose.

The fusion peptides of the present invention may also optionally comprise signal peptides for directing secretion of the fusion peptides from the cell, so that the fusion peptides may readily be isolated from the medium of an active culture of recombinant cells genetically modified to produce the fusion peptides. Such signal peptides are preferably cleavable from the fusion protein by enzymatic cleavage.

Therefore in one embodiment the invention provides a fusion protein comprising a spacer sequence. In another embodiment the invention provides a fusion protein with a spacer sequence that is a proteolytic cleavage site.

In one embodiment, the invention provides a fusion protein selected front pET17b-SD33-ELP1-90-IFNA2bSD (SEQ ID NO: 22), pET17b-SD33-ELP4-60-IFNA2bSD (SEQ ID NO: 23), pET17b-SD34-ELP1-90-IFNA2bSD (SEQ ID NO: 24), pET17b-SD34-ELP4-60-IFNA2bSD (SEQ ID NO: 25), pET17b-SD22-ELP1-90-IFNA2bSD (SEQ ID NO: 26), pET17b-SD22-ELP4-60-IFNA2bSD (SEQ ID NO: 27), pET17b-SD35-IFNA2bSD-ELP1-90 (SEQ ID NO: 28), pET17b-SD35-IFNA2bSD-ELP4-60 (SEQ ID NO: 29), pET17b-SD37-IFNA2bSD-ELP1-90 (SEQ ID NO: 30), pET17b-SD37-IFNA2bSD-ELP4-60 (SEQ ID NO: 31), pET17b-SD31-IFNA2bSD-ELP1-90 (SEQ ID NO: 32) and pET17b-SD31-IFNA2bSD-ELP4-60 (SEQ ID NO: 33).

In another embodiment the invention provides a fusion protein selected from ELP4-60-S-S-Orexin B, ELP4-60-S-S-MMN, ELP4-60-S-S-NPY and ELP4-60-S-S-Gh.

Yet another embodiment of the invention relates to a polynucleotide comprising a nucleotide sequence encoding a fusion protein exhibiting a phase transition, comprising:

-   -   a) at least one target protein or peptide;     -   b) one or more proteins comprising oligomeric repeats of a         polypeptide sequence selected from SEQ ID NOs: 1-17, wherein the         one or more proteins exhibits a phase transition and are joined         to the at least one target protein or peptide of a);     -   c) at least two residues capable of forming a disulfide bond;         and     -   d) optionally, a spacer sequence separating any of the phase         transition protein(s) of b) from any of the target protein(s) or         peptide(s) of a).

The invention in a further aspect relates to a polynucleotide selected from pET17b-SD33-ELP1-90-IFNA2bSD (SEQ ID NO; 34), pET17b-SD33-ELP4-60-IFNA2bSD (SEQ ID NO: 35), pET17b-SD34-ELP1-90-IFNA2bSD (SEQ ID NO: 36), pET17b-SD34-ELP4-60-IFNA2bSD (SEQ ID NO: 37), pET17b-SD22-ELP1-90-IFNA2bSD (SEQ ID NO: 38), pET17b-SD22-ELP4-60-IFNA2bSD (SEQ ID NO: 39), pET17b-SD35-IFNA2bSD-ELP1-90 (SEQ ID NO: 40), pET17b-SD35-IFNA2bSD-ELP4-60 (SEQ ID NO: 41), pET17b-SD37-IFNA2bSD-ELP1-90 (SEQ ID NO: 42), pET17b-SD37-IFNA2bSD-ELP4-60 (SEQ ID NO: 43), pET17b-SD31-IFNA2bSD-ELP1-90 (SEQ ID NO: 44) and pET17b-SD31-IFNA2bSD-ELP4-60 (SEQ ID NO: 45).

In still another embodiment the invention provides an expression vector comprising a polynucleotide encoding a fusion protein of the invention. In yet another embodiment the invention provides a host cell transformed by such an expression vector, where the host cell expresses the fusion protein.

In a still further embodiment, the invention provides an ELP spider complex comprising two or more fusion proteins of the invention, covalently linked by at least one disulfide bond.

The invention also provides a spider complex which includes two or more fusion proteins exhibiting a phase transition comprising:

-   -   a) at least one target protein or peptide;     -   b) one or more proteins comprising oligomeric repeals of a         polypeptide sequence selected from SEQ ID NOs: 1-17, wherein the         one or more proteins exhibits a phase transition and are joined         to the at least one target protein or peptide of a);     -   c) at least two residues capable of forming a disulfide bond;         and     -   d) optionally, a spacer sequence separating any of the phase         transition protein(s) of b) from any of the target protein(s) or         peptide(s) of a).     -   wherein the two or more fusion proteins exhibiting a phase         transition are covalently linked by at least one disulfide bond.

The invention also provides methods of utilizing the fusion proteins and spider complexes as discussed herein.

In one aspect the invention relates to a method of providing a purified protein of interest, comprising contacting a fusion protein comprising the protein of interest and an ELP tag, wherein the fusion protein contains at least one cleavage site that is cleavable to yield the protein of interest as a cleavage product with ELP-TEV1 that is effective to cleave said cleavage site, thereby yielding said protein of interest as a cleavage product in a cleavage product mixture comprising said ELP tag, any uncleaved fusion protein and said ELP-tagged cleavage agent and separating the protein of interest from the cleavage produce mixture by inverse phase transition.

In another aspect the invention provides a method of enhancing proteolytic resistance of a protein or peptide moiety in an ELP-based fusion peptide, comprising provision of the ELP-based fusion peptide in an ELP spider complex form.

Examples of spider complexes discussed herein include Orexin B/ELP and IFNa2bSD/ELP spider constructs, but are broadly applicable to a wide spectrum of other proteins and peptides, and have particular utility for proteins or peptides that are susceptible to proteolytic degradation.

Methods of protection of target proteins or peptides by the spider construct may involve, but are not limited to: (i) slowing or stopping degradative action of proteases, (ii) decreasing or eliminating non-specific associated proteins that may make the target protein or peptide insoluble or prevent the target protein or peptide from properly folding, (iii) increasing the amount of total spider construct concentration in the cell, and/or (iv) exposure of a region of the target protein or peptide subject to proteolysis by the ELP fused to TEV protease when produced in the absence of disulfide bonds. Disulfides formed between ELP and TEV site have been tested. Spacing may be desirably adjusted for such bonding, e.g., with intra-disulfide bonds being separated by at least 2 amino acid residues, such as for example by a -Cys-Cys-moiety. Other techniques for increasing inter- and decreasing intra-disulfide bond formation can be employed.

FIG. 1A is a schematic representation of an ELP fusion protein including a -Cys-Cys-moiety after the ELP and before the TEV site and the peptide. FIG. 1B is a schematic representation of a corresponding spider construct, for pET17b-SD34-ELP4-60-Orexin B (as set forth below in Example 1), and transformation into a BL21 trxB-strain, allowing disulfide bond formation between the fusion proteins to take place in the cytoplasm.

The following examples are intended to illustrate, but not limit the invention.

Example 1 Comparison of ELP-Orexin B Normal Fusion Protein and ELP-Orexin B Spider Construct

Fusion protein constructs of ELP4-60-Orexin B (Normal) and ELP4-60-S-S-Orexin B (Spider) were generated.

FIG. 2 is an SDS-PAGE gel comparison of the two fusion protein constructs. (Lane 1: ELP4-60-Orexin B or ELP4-60-S-S-Orexin B; Lane 2: +ELP1-90-TEV; Lane 3: insolubles following T_(t) (I); and Lane 4: solubles following T_(t) (S)).

FIG. 3 shows an LC-MS analysis of Orexin B derived from ELP4-60-Orexin B (FIG. 3A), in which the level of Orexin B was too low to detect by LC-MS, so that the theoretical location was estimated by location of Orexin B in (B) and ELP4-60-S-S-Orexin B (FIG. 3B), 85% pure, in which the major peak contains the correct molecular weight of Orexin B and the minor peak is a proteolytic fragment of Orexin B.

The original ELP4-60-Orexin B appeared to purify well, however a substantial amount was difficult to resuspend and purify away from insoluble contaminates. Only a portion of Orexin B was cleaved following 18 hr digestion with ELP1-90-TEV. Once cleaved 50% was insoluble following final transition to eliminate uncleaved ELP4-60-Orexin D, ELP1-90-TEV and ELP4-60. The level of Orexin B was too low to analyze by LC-MS. Loading the gel with 10× more cleaved ELP4-60-Orexin B indicated proteolysis had occurred prior to or during cleavage.

ELP4-60-S-S-Orexin B was much easier to purify away from contaminates. Complete cleavage occurred following 18 hr digestion with ELP1-90-TEV. A minor amount of Orexin B remained insoluble following the final transition to eliminate uncleaved ELP4-60-Orexin B, ELP1-90-TEV, and ELP4-60. LC-MS analysis indicated the largest peak contained the correct molecular weight Orexin B peptide and was 85% of total peaks. The minor peak was a proteolytic fragment of Orexin B.

The fusion protein constructs of ELP4-60-Orexin B (Normal) and ELP4-60-S-S-Orexin B (Spider) were expressed in E. coli strains BL21 and trxB. The results are summarized in FIG. 4. FIG. 4 is an SDS-PAGE gel analysis, showing that use of a spider construct influences the amount of purification, the cleavage with ELP4-60-TEV and proteolysis. All samples in the comparison were reduced with DTT prior to loading on the SDS-gel.

It can be seen in FIG. 4 that in both BL21 and trxB, more spider constructs (lanes 2, 4, 6, 8) were produced than normal constructs (lanes 1, 3, 5, 7). Disulfide bond formation within the cytoplasm did not influence the amount of spider construct made. The addition of DTT during purification (lanes 6, 8) did not influence the amount of spider construct purified in the absence of DTT (lanes 2,4). Cleavage with ELP1-90-TEV was not complete when spider constructs were produced in BL21* and purified in the absence of DTT (lane 2). Spider constructs were degraded when produced in BL21* and exposed to OTT during purification (lane 6). The presence of disulfide bonds during expression produced more cleaved Orexin B (lanes 4,8).

Example 2 Spider Constructs of Additional Peptides

FIG. 5 is an SDS-PAGE gel analysis of ELP-spider constructs of three peptides: MMN, NPY and Gh. For each peptide, the lanes are as follows: Lane 1: ELP4-60-S-S-peptide (reduced with DTT): Lane 2: +ELP1-90-TEV; Lane 3: insolubles following T, (I); and Lane 4: solubles following T_(t) (S)).

Comparison of spider constructs and normal constructs were as follows:

MMN peptide: ELP4-60-MMN (58 mg/liter) was not difficult to purify and resulted in 6 mg/liter MMN. ELP4-60-S-S-MMN (180 mg/liter) was not difficult to purify and resulted in 13 mg/liter MMN. It can be seen that use of spider constructs increased the amount of MMN purified.

NPY peptide: ELP4-60-NPY (62 mg/liter) was not difficult to purify and resulted in 7 mg/liter NPY. ELP4-60-S-S-NPY (222 mg/liter) was not difficult to purify and resulted in 20 mg/liter NPY. It can be seen that use of spider constructs increased the amount of NPY purified, it being noted that NPY does not stain well.

Gh peptide: ELP4-60-GH was difficult to purify and resulted in 0 mg/liter Gh. ELP4-60-S-S-GH was not as difficult to purify and resulted in approx 2 mg/liter Gh. A spider construct only partially eliminated Gh degradation. The amount of non-degraded Gh was too low for LC-MS determination. These factors were exacerbated by ELP4-60-Gh transitioning at room temperature (RT):

-   -   a. ELP4-60-GH had to be diluted 10 fold compared to MMN and NPY         to prevent transitioning at RT during cleavage with ELP1-90-TEV.     -   b. The 10-fold dilution made the final concentration of GH too         low for LC-MS analysis.     -   c. Incomplete cleavage with ELP1-90-TEV may be due to a fraction         of ELP4-60-GH that continued to transition at RT even after a 10         fold dilution.     -   d. The low transition temperature of ELP4-60-GH may also be due         to contaminants that could not be eliminated through 3         temperature transitions.

It can be seen that use of spider constructs increased the amount of Gh purified.

With all three peptides (MMN, NPY and Gh), use of spider constructs may also act to buffer the possible toxic effect of the peptide and allow more ELP-peptide to be produced per cell, in addition to decreasing protcolysis.

FIG. 6 shows LC-MS analysis for non-spider peptides. MMN from ELP4-60-S-S-MMN: 99.3% pure 13 mg/L (FIG. 6A) and NPY from ELP4-60-S-S-NPY: 98.1% pure 20 mg/L (FIG. 6B).

FIG. 7 shows LC-MS analysis for pro-CT from ELP1-90-pro-CT: 98.0% pure (FIG. 7A) and Leptin from ELP1-90-Leptin: 85% pure (FIG. 7B).

Example 3 Construction of pET17b-SD35-ELP

SD 35 forward and reverse oligos were annealed, forming 5′ XhoI and 3′ StyI overhangs:

SD35 forward oligo: (SEQ ID NO: 46) TCGAGAACCTGTATTTCCAGGGCGGGTGCTGCGGC SD35 reverse oligo: (SEQ ID NO: 47) CTTGGCCGCAGCAGCCGCCCTGGAAATACAGGTTC Annealed oligos: (SEQ ID NO: 48)  L  E  N  L  Y  F  Q  G  G  C  C  G  Q  G cTCGAGAACCTGTATTTCCAGGGCGGGTGCTGCGGCcaagg (SEQ ID NO: 49) gagctCTTGGACATAAAGGTCCCGCCCACGACGCCGGTTCc XhoI                                 StyI

The annealed SD35 oligos were ligated into pUC19-SD31-ELP, digested with XhoI and StyI and 5′ dephosphorylated with CIP to create pUC19-SD35-ELP. The pUC19-SD35-ELP XbaI-EcoRI fragment containing SD35-ELP was subcloned into pET17b, digested with XbaI and EcoRI and 5′ dephosphorylated with CIP.

In this spider construct, the Cys-Cys is placed following the TEV cleavage site at the amino terminus of the ELP to create a protein/peptide-ELP orientation.

Individual spider constructs pET17b-SD35-ELP1-90 (SEQ ID NO: 50) and pET17b-SD35-ELP4-60 (SEQ ID NO: 51) were created.

Example 4 Construction of pET17b-SD37-ELP

SD37 forward and reverse oligos were annealed, forming BglI and NheI overhangs:

SD37 forward oligo: TGGCCTTGCTGCTGATAAG (SEQ ID NO: 52) SD37 reverse oligo: CTAGCTTATCAGCAGCAAGGCCAGCC (SEQ ID NO: 53) Annealed oligos:   P  G  W  P  C  C  *  *  A  S (SEQ ID NO: 54) gccgggcTGGCCTTGCTGCTGATAAGctagc cggcCCGACCGGAACGACGACTATTCGATCg (SEQ ID NO: 55) BglI                       NheI

The annealed SD37 oligos were ligated into pET17b-SD31-ELP, digested with BglI and NheI and 5′ dephosphorylated with CIP to create pET17b-SD37-ELP.

In this spider construct, the Cys-Cys is placed at the carboxyl terminus of the ELP to create a protein/peptide-ELP orientation.

Individual spider constructs pET17b-SD37-ELP1-90 (SEQ ID NO: 56) and pET17b-SD37-ELP4-60 (SEQ ID NO: 57) were created.

Example 5 Construction of pET17b-SD33-ELP

SD33 forward and reverse oligos were annealed to form XbaI and NcoI overhangs: SD33 forward oligo:

SD33 forward oligo: CTAGAAATAATTTTGTTTAACTTTAAGAAGGAGATATACCATGTGCTGCCC (SEQ ID NO: 58) SD33 reverse oligo CATGGGGCAGCACATGGTATATCTCCTTCTTAAAGTTAAACAAAATTATTT   (SEQ ID NO: 59) Annealed oligos:                                           M  C  C  P  M  G (SEQ ID NO: 60) tCTAGAAATAATTTTGTTTAACTTTAAGAAGGAGATATACCATGTGCTGCCCcatgg agatcTTTATTAAAACAAATTGAAATTCTTCCTCTATATGGTACACGACGGGGTACc (SEQ ID NO: 61) XbaI                                                NcoI

The annealed SD33 oligos were ligated into pET17b-SD22-ELP digested with XbaI and NcoI and 5′ dephosphorylated with CIP to create pET17b-SD33-ELP.

In this spider construct, the Cys-Cys is placed at the amino terminus of the ELP to create an ELP-protein/peptide orientation.

Individual spider constructs pET17b-SD33-ELP1-90 (SEQ ID NO: 62) and pET176-SD33-ELP4-60 (SEQ ID NO: 63) were created.

Example 6 Construction of pET17b-SD34-ELP

SD34 forward and reverse oligos were annealed to form BglI and EcoRV overhangs:

SD34 forward oligo: TGCCCGTGCTGCAGCAGCGGTGAT (SEQ ID NO: 64) SD34 reverse oligo: ATCACCGCTGCTGCAGCACGGCCAGCC (SEQ ID NO: 65)

The annealed SD34 oligos were ligated into pET17b-SD22-ELP digested with BglI and EcoRV and 3′ dephosphorylated to create pET17b-SD34-ELP.

In this spider construct, the Cys-Cys is placed at the carboxyl terminus of the ELP to create an ELP-protein/peptide orientation.

Individual spider constructs pET17b-SD34-ELP1-90 (SEQ ID NO: 68) and pET17b-SD34-ELP4-60 (SEQ ID NO: 69) were created.

Example 7 Construction of Spider Constructs Containing IFNa2bSD

PCR amplification was used to generate the following DNA fragments from a Human cDNA library containing IFNA2b:

IFNa2bSD NdeI-XhoI containing STOP codon:

(SEQ ID NO: 70)                                              CATAT 5150 GTGTGATCTGCCTCAAACCCACAGCCTGGGTAGCAGGAGGACCTTGATGC 5200 TCCTGGCACAGATGAGGAGAATCTCTCTTTTCTCCTGCTTGAAGGACAGA 5250 CATGACTTTGGATTTCCCCAGGAGGAGTTTGGCAACCAGTTCCAAAAGGC 5300 TGAAACCATCCCTGTCCTCCATGAGATGATCCAGCAGATCTTCAATCTCT 5350 TCAGCACAAAGGACTCATCTGCTGCTTGGGATGAGACCCTCCTAGACAAA 5400 TTCTACACTGAACTCTACCAGCAGCTGAATGACCTGGAAGCCTGTGTGAT 5450 ACAGGGGGTGGGGGTGACAGAGACTCCCCTGATGAAGGAGGACTCCATTC 5500 TGGCTGTGAGGAAATACTTCCAAAGAATCACTCTCTATCTGAAAGAGAAG 5550 AAATACAGCCCTTGTGCCTGGGAGGTTGTCAGAGCAGAAATCATGAGATC 5000 TTTTTCTTTGTCAACAAACTTGCAAGAAAGTTTAAGAAGTAAGGAATAACTCGAG

IFNa2bSD NdeI-XhoI, not containing STOP codon:

(SEQ ID NO: 71)                                              CATAT 5150 GTGTGATCTGCCTCAAACCCACAGCCTGGGTAGCAGGAGGACCTTGATGC 5200 TCCTGGCACAGATGAGGAGAATCTCTCTTTTCTCCTGCTTGAAGGACAGA 5250 CATGACTTTGGATTTCCCCAGGAGGAGTTTGGCAACCAGTTCCAAAAGGC 5300 TGAAACCATCCCTGTCCTCCATGAGATGATCCAGCAGATCTTCAATCTCT 5350 TCAGCACAAAGGACTCATCTGCTGCTTGGGATGAGACCCTCCTAGACAAA 5400 TTCTACACTGAACTCTACCAGCAGCTGAATGACCTGGAAGCCTGTGTGAT 5450 ACAGGGGGTGGGGGTGACAGAGACTCCCCTGATGAAGGAGGACTCCATTC 5500 TGGCTGTGAGGAAATACTTCCAAAGAATCACTCTCTATCTGAAAGAGAAG 5550 AAATACAGCCCTTGTGCCTGGGAGGTTGTCAGAGCAGAAATCATGAGATC 5600 TTTTTCTTTGTCAACAAACTTGCAAGAAAGTTTAAGAAGTAAGGAACTCGAG

IFNA2bSD with stop codon was ligated into pET17b-SD33-ELP, pET17b-SD34-ELP and pET17b-SD22-ELP digested with NdeI and partially digested with XhoI and 5′ dephosphorylated with CIP to create pET17b-SD33-ELP-IFNA2bSD, pET17b-SD34-ELP-IFNA2bSD and pET17b-SD22-ELP-IFNA2bSD respectively.

IFNA2bSD without stop codon was ligated into pET17b-SD35-ELP, pET17b-SD37-ELP and pET17b-SD31-ELP digested with NdeI and partially digested with XhoI and 5′ dephosphorylated with CIP to create pET17b-SD35-IFNA2bSD-ELP, pET17b-SD37-IFNA2bSD-ELP and pET17b-SD31-IFNA2bSD-ELP respectively.

Resulting spider constructs created included pET17b-SD33-ELP1-90-IFNA2bSD (SEQ ID NO: 34), pET17b-SD33-ELP4-60-IFNA2bSD (SEQ ID NO: 35), pET17b-SD34-ELP1-90-IFNA2bSD (SEQ ID NO: 36), pET17b-SD34-ELP4-60-IFNA2bSD (SEQ ID NO: 37), pET17b-SD22-ELP1-90-IFNA2bSD (SEQ ID NO: 38), pET17b-SD22-ELP4-60-IFNA2bSD (SEQ ID NO: 39), pET17b-SD35-IFNA2bSD-ELP1-90 (SEQ ID NO: 40), pET17b-SD35-IFNA2bSD-ELP4-60 (SEQ ID NO: 41), pET17b-SD37-IFNA2bSD-ELP1-90 (SEQ ID NO: 42), pET17b-SD37-IFNA2bSD-ELP4-60 (SEQ ID NO: 43), pET17b-SD31-IFNA2bSD-ELP1-90 (SEQ ID NO: 44) and pET17b-SD31-IFNA2bSD-ELP4-60 (SEQ ID NO: 45). Protein translations of these spider constructs are SEQ ID NOs: 22-33.

Example 8 Purification of ELP Spider Proteins

E. coli strain BL21trxB-(DE3) F-ompT hsdSB(rB-mB-) gal dcm trxB15::kan (DE3) (Novagen) containing the ELP/protein construct was inoculated into 5 ml TB supplemented with 100 mM proline, 4% glycerol, phosphate buffer and ampicillin. Cultures were grown for 5 hrs at 37° C. before being transferred at 1:100 dilutions into the same media and grown for 43 hrs at 25° C. unless otherwise noted. The cultures were harvested and resuspended in 10 ml/gram wet weight in the following buffer: 50 mM Tris pH7.0, 1 mM EDTA. Cells were lysed by ultrasonic disruption on ice for 3 minutes, consisting of 15 second bursts at 60 W separated by 15 second cooling down intervals (Sonicate). Cell debris was removed by centrifugation at 20,000 g at 4° C. for 30 minutes. The insoluble pellet was resuspended in the original buffer and volume (Pellet). Soluble material comprised lysate. Inverse temperature transition was induced by adding NaCl to a final concentration of 1.0-2.0 M to the lysate at 25° C., followed by centrifugation at 20,000 g for 15 minutes at 25° C. The resulting pellet contained ELP/protein fusions. The pellet was resuspended in the original volume ice-cold ml buffer, centrifuged at 20,000 g, 4° C. for 15 minutes to remove non-specific insoluble proteins (T,1). The temperature transition cycle was repeated at one additional time to increase the purity of the ELP/protein fusions and reduce the final volume (T,2).

The above purification was performed for spider constructs created in Example 8.

Initially the spider constructs were tested after growth for 15 hours at 25° C. and compared to non-spider protein constructs containing IFNa2bSD to determine which were most likely to produce soluble protein. Results are shown in FIG. 8.

Selected constructs from FIG. 8 were re-expressed for 48 hours at 25° C. and purified using two inverse phase transitions as set forth above. The results of the re-expression are shown in FIG. 9. It can be seen that spider constructs clearly express more initial fusion protein than their non-spider counterparts.

Example 9 ELP1-90-TEV1 Cleavage

In order to purify cleaved protein from ELP, uncleaved protein and protease, the present invention provides an optimized purification of ELP TEV protease (ELP-TEV1) for inverse phase transition removal once cleavage has been completed. ELP1-90-TEV1 was added at a 1:100 dilution of the protein concentration in T,2 and supplemented with 1 mM DTT (T,2+ELP1-90-TEV1). Cleavage was allowed to proceed for 15 hrs at 4° C. Free protein was separated front free ELP and uncleaved ELP/protein fusions by adding 1M NaCl at 25° C., followed by centrifugation at 25° C. Salt transitioned material (ELP and ELP fusions) were resuspended in cold buffer (Insoluble). Salt soluble protein was transferred to a new tube (Soluble). Results can be seen in FIG. 10. Although TEV cleavage was incomplete when performed at 4° C. rather then 25° C., the spider construct not only expressed more soluble ELP fusion protein but also produced 3-4 times more soluble IFNa2bSD following cleavage with ELP1-90-TEV1 and a final transition to separate IFNa2bSD from free ELP, ELP fusions and ELP1-90-TEV1.

Resulting cleaved proteins were as follows:

(SEQ ID NO: 72) pET17b-SD33-IFINA2bSD-ELP1-90, cleaved with TEV: GAHMCDLPQTHSLGSRRILMLLAQMRRISLFSCLKDRHDFGFPQEEFG NQFQKAETIPVLHEMIQQIFNLFSTKDSSAAWDETLLDKFYTELYQQL NDLEACVIQGVGVTETPLMKEDSILAVRKYFQRITLYLKEKKYSPCAW EVVRAEIMRSFSLSTNLQESLRSKE pET17b-SD33-IFNA2bSD-ELP4-60, cleaved with TEV: (SEQ ID NO: 73) GAHMCDLPQTHSLGSRRTLMLLAQMRRISLFSCLKDRHDFGFPQEEFG NQFQKAETIPVLHEMIQQIFNLFSTKDSSAAWDETLLDKFYTELYQQL NDLEACVIQGVGVTETPLMKEDSILAVRKYFQRITLYLKEKKYSPCAW EVVRAEIMRSFSLSTNLQESLRSKE pET17b-SD34-IFNA2bSD-ELP1-90, cleaved with TEV: (SEQ ID NO: 74) GAHMCDLPQTHSLGSRRTLMLLAQMRRISLFSCLKDRHDFGFPQEEFG NQFQKAETIPVLHEMIQQIFNLFSTKDSSAAWDETLLDKFYTELYQQL NDLEACVIQGVGVTETPLMKEDSILAVRKYFQRITLYLKEKKYSPCAW EVVRAEIMRSFSLSTNLQESLRSKE pET17b-SD34-IFNA2bSD-ELP4-60, cleaved with TEV: (SEQ ID NO: 75) GAHMCDLPQTHSLGSRRTLMLLAQMRRISLFSCLKDRHDFGFPQEEFG NQFQKAETIPVLHEMIQQIFNLFSTKDSSAAWDETLLDKFYTELYQQL NDLEACVIQGVGVTETPLMKEDSILAVRKYFQRITLYLKEKKYSPCAW EVVRAEIMRSFSLSTNLQESLRSKE pET17b-SD22-ELP1-90-IFNA2bSD, cleaved with TEV: (SEQ ID NO: 76) GAHMCDLPQTHSLGSRRTLMLLAQMRRISLFSCLKDRHDFGFPQEEFG NQFQKAETIPVLHEMIQQIFNLFSTKDSSAAWDETLLDKFYTELYQQL NDLEACVIQGVGVTETPLMKEDSILAVRKYFQRITLYLKEKKYSPCAW EVVRAEIMRSFSLSTNLQESLRSKE pET17b-SD22-ELP4-60-IFNA2bSD, cleaved with TEV: (SEQ ID NO: 77) GAHMCDLPQTHSLGSRRTLMLLAQMRRISLFSCLKDRHDFGFPQEEFG NQFQKAETIPVLHEMIQQIFNLFSTKDSSAAWDETLLDKFYTELYQQL NDLEACVIQGVGVTETPLMKEDSILAVRKYFQRITLYLKEKKYSPCAW EVVRAEIMRSFSLSTNLQESLRSKE pET17b-SD35-IFNA2bSD-ELP1-90, cleaved with TEV: (SEQ ID NO: 78) MCDLPQTHSLGSRRTLMLLAQMRRISLFSCLKDRHDPGFPQEEFGNQF QKAETIPVLHEMIQQIFNLFSTKDSSAAWDETLLDKFYTELYQQLNDL EACVIQGVGVTETPLMKEDSILAVRKYFQRITLYLKEKKYSPCAWEVV RAEIMRSFSLSTNLQESLRSKELENLYFQ pET17b-SD35-IFNA2bSD-ELP4-60, cleaved with TEV: (SEQ ID NO: 79) MCDLPQTHSLGSRRTLMLLAQMRRISLFSCLKDRHDFGFPQEEFGNQF QKAETIPVLHEMIQQIFNLFSTKDSSAAWDETLLDKFYTELYQQLNDL EACVIQGVGVTETPLMKEDSILAVRKYFQRITLYLKEKKYSPCAWEVV RAEIMRSFSLSTNLQESLRSKELENLYFQ pET17b-SD37-IFNA2bSD-ELP1-90, cleaved with TEV: (SEQ ID NO: 80) MCDLPQTHSLGSRRTLMLLAQMRRISLFSCLKDRHDFGFPQEEFGNQF QKAETIPVLHEMIQQIFNLFSTKDSSAAWDETLLDKFYTELYQQLNDL EACVIQGVGVTETPLMKEDSILAVRKYFQRITLYLKEKKYSPCAWEVV RAEIMRSFSLSTNLQESLRSKELENLYFQ pET17b-SD37-IFNA2bSD-ELP4-60 cleaved with TEV: (SEQ ID NO: 81) MCDLPQTHSLGSRRTLMLLAQMRRISLFSCLKDRHDFGFPQEEFGNQF QKAETIPVLHEMIQQIFNLFSTKDSSAAWDETLLDKFYTELYQQLNDL EACVIQCVGVTETPLMKEDSILAVRKYFQRITLYLKEKKYSPCAWEVV RAEIMRSFSLSTNLQESLRSKELENLYFQ pET17b-SD31-IFNA2bSD-ELP4-60, cleaved with TEV: (SEQ ID NO: 82) MCDLPQTHSLGSRRTLMLLAQMRRISLFSCLKDRHDFGFPQEEFGNQF QKAETIPVLHEMIQQIFNLFSTKDSSAAWDETLLDKFYTELYQQLNDL EACVIQGVCVTETPLMKEDSILAVRKYFQRITLYLKEKKYSPCAWEVV RAEIMRSFSLSTNLQESLRSKELENLYFQ pET17b-SD31-IFNA2bSD-ELP4-60, cleaved with TEV: (SEQ ID NO: 83) MCDLPQTHSLGSRRTLMLLAQMRRISLFSCLKDRHDFGFPQEEFGNQF QKAETIPVLHEMIQQIFNLFSTKDSSAAWDETLLDKFYTELYQQLNDL EACVIQGVCVTETPLMKEDSILAVRKYFQRITLYLKEKKYSPCAWEVV RAEIMRSFSLSTNLQESLRSKELENLYFQ

While the invention has been has been described herein in reference to specific aspects, features and illustrative embodiments of the invention, it will be appreciated that the utility of the invention is not thus limited, but rather extends to and encompasses numerous other variations, modifications and alternative embodiments, as will suggest themselves to those of ordinary skill in the field of the present invention, based on the disclosure herein. Correspondingly, the invention as hereinafter claimed is intended to be broadly construed and interpreted, as including all such variations, modifications and alternative embodiments, within its spirit and scope. 

1. A fusion protein exhibiting a phase transition, comprising: a) at least one target protein or peptide; b) one or more proteins comprising oligomeric repeats of a polypeptide sequence selected front SEQ ID NOs: 1-17, wherein the one or more proteins exhibits a phase transition and are joined to the at least one target protein or peptide of a); c) at least two residues capable of forming a disulfide bond; and d) optionally, a spacer sequence separating any of the phase transition protein(s) of b) from any of the target protein(s) or peptide(s) of a).
 2. The fusion protein of claim 1, wherein the target protein is IFNa2b.
 3. The fusion protein of claim 1, wherein the target peptide is Orexin-B, MMN, NPY or Gh.
 4. The fusion protein of claim 1, wherein the phase transition protein is selected from the group consisting of: SEQ ID NOs: 1, 2, 8, 9, 10, 11, 12, 13, 14, 15, 16, and
 17. 5. The fusion protein of claim 1, wherein the phase transition protein is selected from the group consisting of: SEQ ID NOs: 1, 2, 9, 10, 11, 12, 13, 14, 15, 16, and
 17. 6. The fusion protein of claim 1, wherein the phase transition protein is selected from the group consisting of: ELP1-90, ELP1-180, ELP2-64, ELP2-128, ELP3-72, ELP3-144, ELP4-60, ELP4-120, ELP5-15, ELP5.30, ELP5-60, ELP6-15, ELP6-30, ELP6-60, ELP7-13, ELP7-30 and ELP7-60.
 7. The fusion protein of claim 1, wherein the phase transition is mediatable by an agency comprising one or more of: changing temperature; changing pH; addition of solutes and/or solvents; side chain ionization or chemical modification; and changing pressure.
 8. The fusion protein of claim 1, wherein the at least two residues capable of forming a disulfide bond comprise cysteine.
 9. The fusion protein of claim 1, comprising said spacer sequence.
 10. The fusion protein of claim 9, wherein said spacer sequence comprises a proteolytic cleavage site.
 11. The fusion protein of claim 1, selected from pET17b-SD33-ELP1-90-IFNA2bSD (SEQ ID NO: 22), pET17b-SD33-ELP4-60-IFNA2bSD (SEQ ID NO: 23), pET17b-SD34-ELP1-90-IFNA2bSD (SEQ ID NO: 24), pET17b-SD34-ELP4-60-IFNA2bSD (SEQ ID NO: 25), pET17b-SD22-ELP1-90-IFNA2bSD (SEQ ID NO: 26), pET17b-SD22-ELP4-60-IFNA2bSD (SEQ ID NO: 27), pET17b-SD35-IFNA2bSD-ELP1-90 (SEQ ID NO: 28), pET17b-SD35-IFNA2bSD-ELP4-60 (SEQ ID NO: 29), pET17b-SD37-IFNA2bSD-ELP1-90 (SEQ ID NO: 30), pET17b-SD37-IFNA2bSD-ELP4-60 (SEQ ID NO: 31), pET17b-SD31-IFNA2bSD-ELP1-90 (SEQ ID NO: 32) and pET17b-SD31-IFNA2bSD-ELP4-60 (SEQ ID NO: 33).
 12. The fusion protein of claim 1, selected from ELP4-60-S-S-Orexin B, ELP4-60-S-S-MMN, ELP4-60-S-S-NPY or ELP4-60-S-S-Gh.
 13. A polynucleotide comprising a nucleotide sequence encoding the fusion protein of claim
 1. 14. The polynucleotide of claim 13, selected from pET17b-SD33-ELP1-90-IFNA2bSD (SEQ ID NO: 34), pET17b-SD33-ELP4-60-IFNA2bSD (SEQ ID NO: 35), pET17b-SD34-ELP1-90-IFNA2bSD (SEQ ID NO: 36), pET17b-SD34-ELP4-60-IFNA2bSD (SEQ ID NO: 37), pET17b-SD22-ELP1-90-IFNA2bSD (SEQ ID NO: 38), pET17b-SD22-ELP4-60-IFNA2bSD (SEQ ID NO: 39), pET17b-SD35-IFNA2bSD-ELP1-90 (SEQ ID NO: 40), pET17b-SD35-IFNA2bSD-ELP4-60 (SEQ ID NO: 41), pET17b-SD37-IFNA2bSD-ELP1-90 (SEQ ID NO: 42), pET17b-SD37-IFNA2bSD-ELP4-60 (SEQ ID NO: 43), pET17b-SD31-IFNA2bSD-ELP1-90 (SEQ ID NO: 44) and pET17b-SD31-IFNA2bSD-ELP4-60 (SEQ ID NO: 45).
 15. An expression vector comprising the polynucleotide of claim
 13. 16. A host cell transformed by the vector of claim 15, wherein said host cell expresses the fusion protein.
 17. An ELP spider complex comprising two or more fusion proteins of claim 1, linked by at least one disulfide bond.
 18. An ELP spider complex comprising two or more fusion proteins exhibiting a phase transition, comprising: a) at least one target protein or peptide; b) one or more proteins comprising oligomeric repeats of a polypeptide sequence selected from SEQ ID NOs: 1-17, wherein the one or more proteins exhibits a phase transition and are joined to the at least one target protein or peptide of a); c) at least two residues capable of forming a disulfide bond; and d) optionally, a spacer sequence separating any of the phase transition protein(s) of h) from any of the target protein(s) or peptide(s) of a). wherein the two or more fusion proteins exhibiting a phase transition are linked by at least one disulfide bond.
 19. A method of providing a purified protein of interest, comprising: contacting a fusion protein comprising the protein of interest and an ELP tag, wherein the fusion protein contains at least one cleavage site that is cleavable to yield the protein of interest as a cleavage product with ELP-TEV1 that is effective to cleave said cleavage site, thereby yielding said protein of interest as a cleavage product in a cleavage product mixture comprising said ELP tag, any uncleaved fusion protein and said ELP-tagged cleavage agent; and separating the protein of interest from the cleavage product mixture by inverse phase transition.
 20. The method of claim 19, wherein the fusion protein comprises a spider construct.
 21. A method of enhancing proteolytic resistance of a protein or peptide moiety in an ELP-based fusion peptide, comprising provision of the ELP-based fusion peptide in an ELP spider complex.
 22. An ELP fusion protein spider complex. 